Water treatment on a fast filter with a sandy single-layer load
Sand, being a natural and completely safe mineral for humans and having a fine-grained structure, has been used as a filter material for many years.
Sand-loaded filters are the most common in water purification systems; they can work both independently, clarifying water to standard levels, and in combination with iron removal, softening or disinfection, if necessary.
The determining factors when choosing a filter housing and its loading are, as already mentioned, the required throughput of the purification system and the quality of the water at the inlet and outlet.
For quarry screened sand with a fraction of 0.5-1.2 mm (equiv. 0.7-0.8 mm), most commonly used in industrial water treatment plants, the operating conditions will be as follows:
- Effective filtration rate: 5-6 m/h (cf. 5.5 m/h);
forced: 6.0-7.5 m/h.
(The forced filtration rate is set in case of emergency, in the event that one or more filters go into repair, with a sharp increase in water consumption and in other cases in which it becomes necessary to increase the flow of water through a short period of time). - Suspended solids concentration: no more than 50 mg/l.
- Layer height: not less than 0.7-0.8 m.
- The regeneration period is not less than 1 time in 7 days, but not more than 1 time in 8-12 hours in normal mode, and not more than 1 time in 6 hours in forced mode.
- Washing intensity: 12-16 l/(cm2);
- Backwash duration: 20 (8) min;
- Direct flush duration: 2 min;
- The value of the relative expansion of the load: 45% - according to SNiP, in practice it is allowed in fast pressure filters made of fiberglass up to 30%.
- Limit pressure loss should not exceed 6.0-8.0 m (0.6-0.8 atm.), i.e. pressure drop should not be more than 0.8 atm.
- Dirt capacity: 0.75 kg/m3, without preliminary settling and coagulation.
- Adding a coagulant: with permanganate oxidation above 8 mgO / l and color more than 20 degrees.
For sand with a fraction of 0.7-1.6 mm (equiv. 0.8-1.0 mm), used where the quality of the filtrate with a given sand fraction will meet the required parameters:
- Effective filtration rate in normal mode: 6.0-8.0 m/h (cf. 7.0 m/h),
forced: 7-9.5 m/h. - Layer height: not less than 1.3-1.5 m.
- Regeneration period: not less than 1 time in 7 days, but not more than 1 time in 8-12 hours in normal mode, and not more than 1 time in 6 hours in forced mode.
- Washing intensity: 14-16 l/(s m2);
- Backwash duration: 5-6 min;
- Direct flush duration: 2 min;
- The value of the relative expansion of the load: 30%.
- Dirt capacity: 0.75 kg/m3, without preliminary settling and coagulation.
